Regarded as the seed of any form of life, the cell is a complex and stunning system capable of performing a great variety of tasks. In order to properly complete its functionalities, precise mechanisms of control are necessary during the cell life (i.e. the cell cycle). Among them, great importance is given to the ones related to size homeostasis; indeed, experimental evidence has shown that size is cell type-specific and is important in monitoring cell function. The actual state of knowledge in the field has identified three main 'checkpoints' for this regulation: the reduction or starting point, at the G1/S transition, which defines the border between growth and DNA replication; a checkpoint at the G2/M transition, which is related to the division between the pre-mitotic phase and the mitotic one; and the spindle checkpoint that ensures the correct progress of the mitotic phase.